As is well known in the art, acoustic feedback occurs when some of the amplified sound leaks from the ear canal and is picked up by the ITE hearing aid microphone and then re-amplified. This starts the cycle of leakage and re-amplification (the “feedback loop”) that results in the squeal and/or whistle we know as “acoustic feedback.”
A traditional solution for reducing acoustic feedback has been to increase the acoustic seal in the ear canal, usually by fabricating tighter, longer, but often more uncomfortable ear molds. For some hearing-impaired people, particularly those with moderate or moderate-to-severe hearing losses, this may take care of the problem. However, there is a limit to the amount of sound isolation that any ear mold can provide; even with the tightest mold; given enough amplification, sound is going to leak from the ear canal and will start the feedback cycle.
A contemporary solution for reducing acoustic feedback associated with open ITE hearing aids is to employ digital signal processing to determine whether a portion of the amplified signal contains elements that have the acoustic characteristics of acoustic feedback. If an acoustic signal does comprise characteristics of acoustic feedback, the feedback circuit first determines the frequency, amplitude, and phase of the feedback component and then generates signals of opposite phase that will cancel (or markedly reduce) the feedback component.
However, since acoustic feedback is often a complex signal (like a tone with a series of harmonics), the cancellation process requires a complex solution, since more than one frequency is involved. This has to be done very quickly and has to be done adaptively. Thus, a disadvantage to this technique is that digital processing methods often eliminate desirable acoustic signals along with the acoustic feedback signal resulting in transmitted audio signal distortion.
There is a continuing need for enhanced systems and methods for reducing acoustic feedback interference signals associated with non-occluding, i.e. open ITE, hearing aids.